The present invention relates to a rectangular air battery with an excellent resistance to electrolyte leakage.
Air button batteries are used as the driving power sources for miniature hearing aids, small-sized pagers, etc. Since air batteries need no bulky positive electrode active material, they can accommodate more zinc, which is the negative electrode active material, than other batteries of the same size, for example, silver oxide batteries. Therefore, they have an advantage of having a large battery capacity. On the other hand, air button batteries have a drawback in that the current to be drawn therefrom is small. This drawback makes difficult the use of the batteries as the driving power sources for small-sized electronic equipment, such as portable electronic devices and small-sized audio equipment.
The current to be drawn from air button batteries can be increased by enlarging battery size. However, merely enlarging battery size involves a problem in that enlarged batteries do not fit into the battery mounting space in small-sized electronic devices.
Such problems can be addressed by the following two measures. The first measure is a method of decreasing internal resistance, to increase the current to be drawn. The second one is a method of employing a rectangular shape, instead of the button shape, to make effective use of the battery mounting space in small-sized electronic devices, in order to increase the current to be drawn. International Publication No. WO 00/36693 proposes using a rectangular first case, a rectangular second case, and an insulating gasket, and sealing the first case and the second case with the insulating gasket that is interposed therebetween.
Unlike the button battery, the above-described rectangular air battery has a shape consisting of linear parts and corner parts, thereby presenting the following problems upon sealing.
Since the second case is produced by a drawing process, the corner parts have uneven thickness and undergo work hardening. Thus, the corner parts of the second case have an increased mechanical strength, compared with the linear parts. Because of the difference in mechanical strength between the corner parts and the linear parts, when the battery is sealed by crimping, i.e, by applying a pressure that is suitable for the mechanical strength of the corner parts, the linear parts cannot withstand the sealing pressure, so that the sidewalls of the linear parts buckle and deform inward (See FIG. 11). This causes two additional problems.
The first problem is the creation of gaps between the sidewalls of the linear parts of the second case and the insulating gasket, through which an electrolyte leaks. The second problem is the creation of gaps between the peripheral edge of the air electrode and the inner walls of the first case, which results in poor contact between them and therefore in increased internal resistance of the battery.
The present invention solves these conventional problems and aims to provide a rectangular air battery with an excellent resistance to electrolyte leakage which is capable of preventing a rise in internal resistance.